The invention relates generally to the field of equipment that incorporates multiple mandrels for temporarily receiving work pieces upon which a process must be performed, where it is sometimes necessary to quickly retract or reposition a mandrel. More particularly, the invention relates to such equipment wherein the mandrel needs to be retracted in a direction perpendicular to the longitudinal axis of the mandrel.
A mandrel is typically a cylindrical member used to retain another object during a processing operation. For example, in typical equipment used in the printing of beverage cans, a large number of freely rotating mandrels are mounted about the perimeter of a large rotating drum. A blank can is placed onto each mandrel at a loading station, and the drum then rotates the loaded mandrel past an applicator or printing mechanism, such as a rotating wheel having a series of inked printing blankets. The can loaded onto the mandrel contacts the printing blanket and ink is transferred in a precise manner. After inking, a varnish or lacquer is often applied as a sealant in the same manner. This type of equipment is designed to handle large quantities of cans in a very short time. For example, a typical decorating machine of the type described having from 24 to 36 equally spaced mandrels may produce over 2000 printings per minute.
In the event a can is not properly loaded onto a mandrel, ink or varnish will transfer onto the mandrel itself due to the thinness of the can wall and the minimal tolerances present in the equipment. If this occurs, ink or varnish will be transferred to the interior of the next blank can loaded onto the mandrel unless the equipment is shut down and cleaned. Where production totals of hundreds of thousands of cans per day are required, a shut down for even a few minutes is costly.
Because of this, when a blank can is not properly loaded onto a mandrel, the decorating machine is designed to detect this condition by known sensing means and to trigger a trip or can skip event. The trip event typically consists of the rotating applicator drum or the can handling component being shifted slightly away from the printing blanket component so that ink is not transferred onto an empty mandrel. In current equipment, a trip event may result in incomplete printing of 3 or more cans preceding and following the empty mandrel, such that these cans will be rejected by quality control. In addition, the current mechanism for enacting the trip event requires movement of large sections of the equipment, which entails complicated mechanisms that are susceptible to failure and wear. Examples of trip structures and systems designed to address the problem of unloaded or misloaded mandrels are shown in U.S. Pat. No. 3,665,853 to Hartmeister et al., U.S. Pat. No. 4,441,418 to Hahn, and U.S. Pat. No. 4,491,613 to Hahn, which show equipment wherein the applicator or printing means is retracted in response to occurrence of a trip event, and U.S. Pat. No. 3,563,170 to Cvacho et al., U.S. Pat. No. 3,851,579 to Zurick, U.S. Pat. No. 4,018,151 to Urban et al., and U.S. Pat. No. 4,037,530 to Sirvet, which show equipment wherein the mandrel support means is retracted in response to the trip event. These patents provide an overview of the general problem and descriptions of representative equipment found in the industry, and therefore the disclosure of these references is incorporated herein by reference.
The mechanisms utilized in the known art to retract either the mandrel support members or the printing members are excessively complicated and prone to mechanical failure or failure due to misadjustment, typically utilized pivoting arms, spring members and the like that require the entire mandrel support members to move relative to the rotating drum upon which they are mounted. It is an object of this invention to provide an independent mandrel trip apparatus having an operational mechanism of improved efficiency and durability, wherein a trip event only affects the non-loaded mandrel, in that each mandrel mounting block is provided with means to retract its mandrel without effect to the adjacent mandrels. It is a further object to provide such an apparatus wherein the mounting blocks are directly fixed to the rotating drum without need to provide for movement of the mounting block relative to the drum, and wherein the mandrel mounting means can be readily retrofitted onto existing decorating machines or the like. These objects, along with objects not expressly set forth in this section, will become apparent from the disclosure to follow.